The present invention relates to pintle-type valves; more particularly to axially-operative pintle shaft valves for permitting the controlled admission of exhaust gases into the fuel intake manifold of an internal combustion engine; and most particularly to such a valve having an annular shaft brush for preventing coking of the portion of the pintle shaft which engages the shaft bearing, thereby preventing coking product from entering the bearing and causing seizure of the shaft.
It is well known in the automotive art to provide a variable valve connecting the exhaust manifold with the intake manifold of an internal combustion engine to permit selective and controlled recirculation of a portion of an engine""s exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the burn temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve.
Typically, an EGR valve has a valve body enclosing a chamber disposed between a first port in the exhaust manifold and a second port in the intake manifold; a valve seat dividing the chamber between the two ports; a valve pintle shaft having a valve head fitted to the valve seat and extending from the valve head through a bearing mounted in a third port in a sidewall of the valve body; a spring-retained bearing splash shield; and a solenoid actuator mounted on the exterior of the valve body and operationally connected to the outer end of the valve pintle.
A problem inherent to EGR valve applications is that the managed fluid (exhaust gas) is moisture-laden, corrosive, and dirty with particulates. Especially in diesel engines, the exhaust gas can form coke-like deposits, known generally as coking, on surfaces exposed to these materials including the valve chamber walls and the head-actuating pintle shaft. The pintle shaft typically passes through a journal bearing disposed in a wall of the valve body which provides radial support and axial guidance to the shaft. To minimize gas leakage along the shaft, the clearance between the bore in the bearing and the pintle shaft typically is made as small as is practical without causing significant drag on the axial actuation of the pintle by the external actuator. If the valve is normally closed, as is typical, a protected and clean portion of the pintle shaft within the bearing bore must become extended into the valve chamber when the pintle is actuated to open the valve and admit exhaust gas into the valve chamber. The clean portion of the pintle shaft may become coked, which coking material will be drawn into the bearing bore when the valve is closed. Thus, a typical EGR valve is undesirably vulnerable to becoming seized and inoperative by coking of the pintle shaft during operation.
What is needed is a device which may be fitted to an EGR valve that significantly reduces or eliminates coking of the valve shaft without impairing efficiency, size, and performance of the valve and actuator. Preferably, such a device is simple and inexpensive to fabricate and install.
The present invention is directed to an annular metal-bristled brush for cleaning the pintle shaft of a pintle valve, such as an exhaust gas recirculation valve for an internal combustion engine, to prevent coking and failure of the valve. The brush surrounds the shaft, the tips of the bristles making contact with the shaft with sufficient force to dislodge incipient coke deposits but with insufficient force to inhibit the axial motion of the pintle shaft in actuation. Preferably, the brush is disposed in an annular space in the valve body between the pintle shaft bearing and the gas-metering chamber such that the shaft is brushed in both directions during each actuative cycle of the valve. Preferably, the annular space is slight larger both axially and radially than the corresponding dimensions of the brush so that the brush is free to float without binding the pintle shaft.